1. Field of the Invention:
This invention relates to a converter for heterogeneous catalytic synthesis under pressure, particularly for the catalystic synthesis of ammonia and menthanol, consisting of an external shell in a single piece and, inside of this, of a cartridge containing catalyst of granule type and various characteristics arranged in one or more beds contained in modular baskets.
2. Description of the Related Art:
It is known that in this type of converters it is important to control the gas temperature at the inlet of the catalytic beds, such a control being preferably obtained in the converters with a higher yield by means of indirect cooling with the use of exchangers.
In converters of radial or axial-radial type already described in numerous patents of the Applicant (see, for example, the Swiss Patent No. 643752), the exchangers used for the control of the gas temperature are generally located in the central part of the catalytic beds, coaxial to the length of the converter itself.
The use of exchangers in converters with various beds (at least two), even if on one side they present the advantage of increasing the functioning yield with respect to the cooling systems between the beds obtained by means of fresh gas "quench", involves, on the other hand, notable constructive complications which render the access to single catalytic beds quite difficult in the catalyst installation and removal phases.
In Swiss Patent 643752, a first simplication was proposed wherein modular cartridges are superposed, each one containing a catalytic bed and, in at least one part of the bed, an exchanger is arranged coaxially with the converter axis.
According to that patent (see FIG. 8 of the text), each modular cartridge incorporated: a) a cylindrical solid external wall that constitutes a section of the external wall of the airspace forming cartridge with the internal wall of the external shell of the converter; b) an external cylindrical wall permeable to gas that constitutes the external distribution gas wall in the catalytic bed and of catalyst container, c) a cylindrical external wall permeable to gas that constitutes the internal gas distribution wall in the catalytic bed and catalyst container, d) a central exchanger (in at least one part of the beds) coaxial with the length of the converter; e) an internal cylindrical wall for the collection of the gas distributed in the external part of the central exchanger tubes; f) a connection and support system located at the ends or extremities of the external solid wall such as to permit the stacking of the single modular cartridges which form the internal cartridge.
The single exchanger located within the beds has its ends or extremities flanged between each other.
The complexity of this system induces the following:
1) even though the single modular cartridges are simply superposed one on each other, they can dissassembled among themselves by simply disconnecting the flanged coupling between the flange at the extremity of the central exchanger;
2) access to connection flanges of the central exchangers is possible only after having emptied the upper bed of all of the catalyst, and by manholes that are located on the bottom of the bed itself;
3) expansion compensators are required in the connection collectors of the exchangers in order to balance the thrusts due to differential expansion of the various parts of the modular cartridges.
This design involves problematic access to the catalytic beds for the removal of the catalyst and the assembly of the cartridge itself (difficulty in installing and removing the catalyst and for the maintenance of the cartridge). In addition, the external wall of the cartridge is contacted by at least one part of the fresh feed gas. This cartridge is not being of one piece, but rather is made of cylindrical sections superposed as described above. Thus, they are susceptible to disalignments due to thermal expansion during use, resulting in imperfect sealing of the coupling of various sections, which may jeopardize the correct functioning and the converter yield (gas bypass).
The Applicant has already proposed a solution that eliminated most of these inconveniences. In Swiss Patent Application 00728/87-5 (see FIG. 2), a cartridge for quench-type converters is described wherein:
a) an external wall of the airspace forming cartridge (with the shell) is a single piece substantially along the axial length of the converter;
b) an external wall forming the beds is completely separate and has no connection whatsoever with the airspace forming wall and is instead made of detached modules each one being delimited in at least one catalytic bed, each module leaning of the module below it; the control of the temperature is, however, carried out here by means of "quench" with fresh gas.